Sliding components have been selected from the viewpoint of good abrasion resistance on the sliding face and low sliding resistance. A single material having excellent properties has been employed or a composite has been prepared therefrom for practical utilization as a sliding component.
Attention has been drawn to ceramics having excellent sliding properties in recent years. Especially, examples of actual use are found in which a ceramic is joined to a metal material in a manner such that the ceramic is positioned in sliding parts where sliding conditions are severe.
For example, there is an application where a silicon nitride ceramic having good sliding properties is joined to a cam sliding portion of an engine tappet as practiced for a high-powered engine or in compliance with exhaust gas regulations.
The above sliding component is occasionally required to exhibit sliding properties at sliding zones other than the ceramic zone or on the whole body of the component, so that hardening treatment is performed for improving the sliding properties of the metal material.
Thus, the metal part is hardened by the use of the heating and cooling effected when the ceramic is joined to the metal by heating in the previous Japanese,Patent Application Laid-Open Nos. 2-55807, 2-55809, 2-199073 and 4-2672.
However, the above hardening relying on the heat joining has encountered the problems that the heating temperature applied to the sliding part of the body is different from that employed in the conventional heat hardening treatment of steel, thereby occasionally disenabling attainment of a hardness required for the sliding performance, and that the cooling method is special, the variety of metallic material suitable therefor is limited and the cost is increased. For example, the above Japanese Patent Application Laid-Open No. 2-55809 describes the use of a specific steel which is capable of being hardened by martensitic transformation induced by air-cooling after the heat joining. Further, in the Japanese Patent Application Laid-Open No. 2-55807, a main body of a tappet is constituted of a top half part of a carburized steel and a bottom half part of another steel and these parts are hardened by the heating and cooling effected when a ceramic member is brazed to the bottom half part. Therefore, a complicated carburization step is required for the top half part before heat-joining the ceramic member to the main body.
With respect to the above mentioned conventional problem, the present invention is directed to provide a method of manufacturing a sliding component of higher practicability.